A 52-year-old man who strangled to death his female friend in a River District apartment pleaded guilty to first-degree domestic-violence manslaughter and was sentenced to 17 years in prison today.

Jim Dwayne Taft — who has in the past been diagnosed with various mental illnesses, including bipolar disorder — for the first time this morning gave a reason for the killing: He thought the victim, Virginia Malvey, 59, was interested in him only because of his Social Security disability income.

It’s an explanation that didn’t make sense to Multnomah County prosecutor Amy Holmes Hehn or members of Malvey’s family, who live on the East Coast and spoke by phone of Malvey’s kindness and willingness to helping others.

The nature of Taft’s relationship with Malvey was unclear, but they had been friends for about 10 years and may have been intimate. Taft was originally charged with domestic-violence murder and strangulation.